Dynamic tuning of internal parameters for solid-state disk based on workload access patterns

ABSTRACT

A system and method for tuning a solid state disk memory includes computing a metric representing a usage trend of a solid state disk memory. Whether one or more parameters need to be adjusted to provide a change in performance is determined. The parameter is adjusted in accordance with the metric to impact the performance of running workloads. These steps are repeated after an elapsed time interval.

BACKGROUND

1. Technical Field

The present invention relates to solid state disks, and moreparticularly to solid state disk memory management to improveperformance and endurance.

2. Description of Related Art

With the evolution of applications that process large amounts of data(e.g., BigData Analytics applications), high-performance and dynamicstorage is becoming a necessity. Support for high-performance dataanalysis is a key ingredient, especially in enterprise systems. Toprovide fast data access (and thereby quick analysis), many enterprisesystems use Solid-State Disks (SSDs).

SSDs are typically made up of flash memory, which has emerged as animportant technology for persistent data storage both for personalcomputers and enterprise systems. An SSD is typically read and writtenin units of pages. Each page is usually 2 k bytes to 4 k bytes. Severalpages (e.g., 64-256 pages) form a block. In addition, Flash memorytypically has a constraint that a block may be written only a certainnumber of times, after which the block becomes invalid. Wear-levelingschemes are provided in SSDs to increase the lifetime of blocks (andhence of the entire SSD).

While SSDs provide efficient read access, writes are more complexbecause in-place updates are not possible in flash memory. Therefore,SSD vendors normally ship SSDs with a layer called the Flash TranslationLayer (FTL) that remaps every write to a different block/page andexposes an SSD as a standard block device (like a hard disk).

SSDs internally maintain translation tables to map received ‘logical’addresses into actual ‘physical’ addresses. As applications run andaccess SSDs, the access pattern continuously results in changes to thesetranslation tables. These tables can be at a block level, page level orhybrid (mix of block and page). A page-level translation scheme providesmaximum lifetime of an SSD (but with increased memory overhead) whereasa block level translation (which occupies much less memory) will provideless lifetime. Hybrid schemes have been proposed as a mix of both theseextremes to provide a better lifetime with less memory.

SUMMARY

A system and method for tuning a solid state disk memory includescomputing a metric representing a usage trend of a solid state diskmemory. Whether one or more parameters need to be adjusted to provide achange in performance is determined. The parameter is adjusted inaccordance with the metric to impact the performance of runningworkloads. These steps are repeated after an elapsed time interval.

Another method for tuning a solid state disk memory includes computing alinearity metric by employing a logical to physical translation table toobtain usage pattern data representing a usage trend of a solid statedisk memory over one or more time intervals; determining whether aparameter needs to be adjusted to provide a change in performance byconsulting a lookup table or formula; and adjusting the parameter inaccordance with the metric to change the performance.

Yet another method for tuning a solid state disk memory includesreceiving access request information in a solid state disk controller;storing the access request information in a translation table; computinga linearity metric, using a regression technique, from the accessrequest information in the translation table to obtain usage patterndata representing a usage trend of a solid state disk memory over one ormore time intervals; determining whether a parameter needs to be tunedto provide increased memory lifetime by consulting a lookup table orformula; adjusting the parameter in accordance with the metric toincrease an overall lifetime of the solid state disk memory; andrechecking whether adjustments are needed after an elapsed timeinterval.

These methods may be performed on a computer readable storage mediumcomprising a computer readable program for tuning a solid state diskmemory, wherein the computer readable program when executed on a solidstate disk controller causes the solid state disk controller to performthe methods steps.

A solid state disk memory system includes a solid state disk controllerhaving a translation layer. The translation layer includes a datastructure for storing access data, a linearity computation moduleconfigured to compute a metric representing a usage trend of a solidstate disk memory using the access data and an adjustment moduleconfigured to determine whether a parameter needs to be adjusted and anamount of adjustment in accordance with the metric to change performanceof the solid state disk memory.

Another solid state disk memory system includes a solid state diskcontroller having a translation layer. The translation layer includes adata structure for storing access data, a linearity computation moduleconfigured to compute a metric representing a usage trend of a solidstate disk memory using the access data and an adjustment moduleconfigured to determine whether a parameter needs to be adjusted and anamount of adjustment in accordance with the metric to change performanceof the solid state disk memory. One or more solid state disks areincludes in the solid state disk memory. The solid state disks aremanaged by the solid state disk controller to increase lifetime of thedisks by distributing usage over the one or more solid state disks.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a block/flow diagram showing a solid state disk memory systemin accordance with one illustrative embodiment;

FIG. 2 is a block/flow diagram showing a flash translation layer of asolid state disk controller in accordance with one illustrativeembodiment;

FIG. 3 is a block/flow diagram showing a flash memory of a solid statedisk in accordance with one illustrative embodiment;

FIG. 4 is a block/flow diagram showing a system/method for tuningparameters in a solid state disk system in accordance with oneillustrative embodiment; and

FIG. 5 is a block/flow diagram showing a system/method for tuningparameters in a solid state disk system in accordance with anotherillustrative embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with the present principles, systems and methods fordynamically tuning internal parameters for solid state disks (SSD) areprovided. The internal parameters may be tuned by analyzing translationmapping tables and computing metrics using, e.g., linear-regressionmodels (such as, e.g., ANOVA, etc.). Adjustments and tuning areimplemented to improve performance and increase endurance of SSDs.

Diversity in today's applications imposes diverse and continuouslychanging demands on a computer system. With applications being sodiverse, dynamic ways of tuning such parameters by capturing thediversity of running workloads' access patterns is useful. Optimizationof an SSD may be provided by setting parameters for individualapplications. This may include pre-fetching, caching, internal SSDwear-leveling parameters (e.g., the number of block-mapped pages versuspage-mapped pages in hybrid Flash Translation Layer (FTL) schemes), etc.

In one embodiment, access patterns of applications in the SSD Flashcontroller can be understood without requiring any user or applicationintervention. This knowledge can be employed to dynamically tune the SSDparameters for higher application performance and/or more SSD endurance.In another embodiment, linearity metrics may be employed. Linearitymetrics capture the access patterns of a workload running on SSD. Theselinearity metrics are simple enough to be computed with reasonablecomputational overhead. Such computations can also be done in thebackground so as to not interfere with a critical SSD access path.

In addition to tuning functional parameters, such as garbage collectionor wear-leveling parameters, the access pattern knowledge can havemultiple uses such as turning on/off various functions, such as,pre-fetching, caching, etc. The present principles also leverage currentfeatures of SSDs. For example, translation tables in SSDs are persistentinformation that the SSD needs to maintain, thus there is negligibleadditional memory/storage requirement to calculate metrics related tothese tables.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing. Computer program code for carrying out operations foraspects of the present invention may be written in any combination ofone or more programming languages, including an object orientedprogramming language such as Java, Smalltalk, C++ or the like andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The program codemay execute entirely on the user's computer, partly on the user'scomputer, as a stand-alone software package, partly on the user'scomputer and partly on a remote computer or entirely on the remotecomputer or server. In the latter scenario, the remote computer may beconnected to the user's computer through any type of network, includinga local area network (LAN) or a wide area network (WAN), or theconnection may be made to an external computer (for example, through theInternet using an Internet Service Provider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks. The computer program instructions may also beloaded onto a computer, other programmable data processing apparatus, orother devices to cause a series of operational steps to be performed onthe computer, other programmable apparatus or other devices to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblocks may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, an illustrative solid statedisk (SSD) memory system 10 is shown in accordance with one illustrativeembodiment. The system 10 includes a SSD controller 12 and one or moreflash memory devices 14. The system 10 may include any number of devicesor systems that employ SSD memory. Such devices may include, e.g.,cameras, video games controllers, video or music players, computers,printers or another device configured to employ SSD memory, e.g., flashmemory. The system 10 includes input/output ports 15 which may beemployed to interact with the controller 12 and memory device 14.

The system 10 may employ a logical page and physical page memorymanagement system. The SSD controller 12 is selectively coupled to oneor more SSD memory devices 14. The controller 12 may include a processoror may work in conjunction with one or more processors 17 of the system10. The controller 12 may include memory or may employ the memory of theSSD memory devices 14.

The controller 12 may include a plurality of mechanisms that assist inmanaging memory storage on and in between SSD devices 14. Thesemechanisms may be implemented at the Flash Translation Layer (FTL) ofthe controller 12. These mechanisms may be employed to provide a moreeven distribution of interactions with the SSD devices 14 resulting inmore even wear and increased memory lifetimes. The mechanisms describedherein may be employed as tunable mechanisms having their use enabled orchanged in accordance with the present principles. It should beunderstood that the tunable parameters used to control these mechanismsare illustrations and should not be considered as limiting. Moreover,other mechanisms in addition to or instead of the illustrated mechanismsare contemplated in accordance with the present principles.

In one embodiment, a log block wear-leveling approach mechanism 20 maybe included and controlled by the controller 12. Most of the SSD deviceis block-mapped. These blocks are referred to as data blocks. A smallnumber of blocks, referred to as log blocks, are page-mapped. The mainpurpose of log blocks is to deal with overwrites to the data blocks.When the first overwrite happens to a page in a data block, a log blockis associated with this data block. The overwritten page in the datablock is invalidated and copied to the first available page in the logblock. Any subsequent overwrites to the same data block are written tothe next available pages in the log block. When all the pages in the logblock are used. The data block and its associated log block are mergedinto a free erased data block. By including the new content (overwrites)to the log block, the data block does not have to be completelydiscarded. This reduces access cycles and wear and increases lifetime ofthe device. To access the new content, the page is accessed and directedto the associated log block.

Another mechanism may include a garbage collector (GC) 24, which may belaunched periodically to recycle invalidated physical pages, consolidatevalid pages into a new erased block, and clean old invalidated blocks. Awear-leveling mechanism 26 may be included to ensure even wear overmemory space. Since writes are often concentrated on a subset of data,which may cause some blocks to wear out earlier than the others, thewear-leveling mechanism 26 tracks and shuffles hot and cold data to evenout writes in flash memory to colder locations to ensure evenlydistributed writing. This results in extended lifetime of the solidstate memory device. These mechanisms and other mechanisms may becontrolled and adjusted in accordance with workload or access patternfeedback as will be set forth in further detail herein.

Referring to FIG. 2, the SSD devices 14 may include a flash memorydevice 100, which is a solid state disk (SSD). Flash device 100 is shownin accordance with an illustrative embodiment, and schematically depictsinternal organization of the flash device 100. The flash device 100 isinternally divided into planes 101. Each plane 101 has a set of blocks102. Each block 102 has a set of pages 104 (there are, e.g., 64 or 128pages per block). Each page 104 has a data area 105 and is alsoassociated with a spare area 106. The flash device 100 can be read fromand written to in a granularity of pages 104, for example.

As compared to a typical Hard Disk drive, flash memory (and an SSDincluding flash memory) has some technical constraints. One constraintincludes that no in-place overwrite is available. A whole block must beerased before writing (programming) any page in a block. Anotherconstraint includes that no random writes are available. The pages in ablock must be written to (programmed) sequentially. There are limitederase or program cycles available. A block can wear out after a certainnumber of erase or program cycles (this may be, say 10⁴ cycles for anMLC Flash and 10⁵ for SLC Flash).

Note that as described herein “block” refers to the Flash Block which ismade up of multiple Flash Pages. Also, “page” refers to a single unit ofwrite (e.g., 2 k/4 k). Each page 104 may include a spare area 106 whereadditional information may be stored. The spare area 106 may be dividedinto regions where additional information and indexes may be stored. Forexample, one region 108 may include error correction codes (ECC) whileanother region may include logical page number (LPN) or other index 110.Additional area is available in region 112.

Referring to FIG. 3, an SSD controller or flash file-system 200 (seealso SSD controller 12, FIG. 1) is illustratively depicted in accordancewith one embodiment. A Flash Translation Layer (FTL) 202 is a componentimplemented in the SSD controller 200 (or a flash file-system) thatworks to address the constraints described above and exposes an array ofLogical Page Addresses (LPAs) or Logical Page Numbers (LPNs) to a host,effectively emulating a standard block device such as provided in harddisk operations. The constraints include, e.g., that no in-placeoverwrite is available, that no random writes are available, limitederase or program cycles are available (limited wear). To address theseconstraints, indirect mapping is provided.

A translation table 204 is maintained in the controller 202 to trackdynamic mapping between logical page numbers (LPNs) and actual physicalpage numbers (PPNs) in a flash memory (100, FIG. 1). It should beunderstood that a translation table is illustrative of one embodiment,and that other devices or structures may also be employed. For example,one can maintain tree structures for the logical-physical mappings orsome other kind of data structures (combination of trees, tables, lists,hash-tables, etc.).

The translation table 204 tracks mappings between logical page addressesand physical pages addresses and server I/O requests 206. Since thesetranslation entries are continuously changing (as indicated, FLASHcannot overwrite to the same page and hence writes to a different pageand updates the translation entry), this table can be used as anindicator of the linearity of a workload. A linearity computation module208 may be used to compute linearity of the translation table 204 toderive linearity metric(s) 216. Linearity metrics refer to a measure ofa linear relationship between two variables or the same variable atdifferent times. For example, these two variables could be the logicalpage addresses and the physical pages addresses of the I/O requests. Inother embodiments, vectors indicating activity may be computed.Computing these vectors may be performed by splitting the translation ormapping table into multiple regions. In some embodiments, these regionscould vary each time.

In other embodiments, the translation table 204 is considered an arrayand linearity is computed using an R² method or linear regression overtwo representative time periods to determine a linearity metric(s) 216,such as a direction vector over time. The direction vector may include anumber from 0 to 1, where 0 indicates that this is a completely randomworkload access pattern and 1 indicates that this is a perfectlysequential workload pattern over time.

In one embodiment, the linearity metrics 216 are determined using alogical to physical (L2P) map (from translation table 204) to identify aworkload pattern. L2P map is always present in the flash memory 100. TheL2P map or mapping table is employed by the SSD controller 200 or memorymanagement unit, to map a logical page onto a physical page. Theoperating system (in a file-system controlled setting) and/or the FTLsoftware running on the controller sets up and controls the L2P map. TheL2P map has a line for each logical page and cross-references physicalpages to the logical pages. Accesses and changes to the L2P map may beaccumulated over a time period, and the activity may be employed todetermine access patterns or workload patterns.

The linearity metrics 216 may be provided to an adjustment module ortuning algorithm 210, which employs the linearity metrics 216 to decidea magnitude and direction (vector) for one or more tuning parameters218. In one embodiment, the tuning parameter 218 indicates a number ofdata blocks 212 versus log blocks 214 in a flash memory 100.

In a particularly useful embodiment, a recent Translations (rT) tablestructure (a subset of the translation table 204) maintains most recentm logical to physical translations of pages that have been recentlyaccessed in the SSD device 100. m is one parameter that can bedynamically adjusted depending on the working set size of runningworkloads.

In one embodiment, the most recent accesses are relevant to calculatethe linearity metric 216 of the workload(s) accessing the SSD device100. Every entry in the rT table may be composed of a (l, p, t) triplet,such that l is a logical page address and p is the correspondingphysical page address in the SSD device and t is the timestamp of a lastaccess to the p page. Anytime a page is accessed for a read or write(requests 206), the corresponding L2P mapping pair is stored in the rTtable 204 (if it is not already there), and the corresponding timestampis updated. If the rT table 204 already has m elements, the oldesttranslation is discarded.

Linear regression is a standard statistical approach used to model therelationship between a scalar dependent variable Y and one or moreexplanatory variables denoted X. A coefficient of determination R²linear regression algorithm may be employed in the linearity computationmodule 208. The R² is a statistical value that gives some informationabout the “goodness of fit”. R² measures how well the regression lineapproximates the real data points. It should be understood that insteadof an R² linear regression algorithm, other metrics may be computed suchas other regression metrics, statistical parameters, etc.

In one example, the linearity computation module 208 may performed bythe following steps to compute linearity metrics. Pseudo code forcomputing the linearity metric 216 may include the following.

Pseudocode for Linearity Computation:

Input: Recent Translation Table, rT

Output: Linearity Metric, LM

Sort the rT table according to the logical addresses, l.

Calculate the R² regression fit of the rT table, where the parameters ofthe linear regression X, and Y are: X: is the set (x₁, x₂, . . . x_(m))of logical addresses in the rT table where x_(i)=l_(i). Y: is the set(y₁, y₂, . . . y_(m)) of corresponding physical addresses in the rTtable where y_(i)=p_(i).

The R2 value is calculated as follows: Calculate the regression line y*using the following.

Least Squares Regression Method:y*=a+bx

The slope b and intercept a are calculated in the following order:

${b = {r\;\frac{{SD}_{y}}{{SD}_{x}}}},$a= Y−b X where

SD_(y) and SD_(x) are the standard deviations of the Y and X setsrespectively,

Y is the mean of the data set Y, and

X is the mean of the data set X.

The mean of the data set is calculated as shown below:

$\overset{\_}{Y} = {\frac{1}{n}{\sum\limits_{i = 1}^{m}y_{i}}}$

The variability of the data sets is measured through different sums ofsquares:

${{SS}_{tot} = {\sum\limits_{i}\left( {y_{i} - \overset{\_}{Y}} \right)^{2}}},$the total sum of squares.

${{SS}_{reg} = {\sum\limits_{i}\left( {y^{*} - \overset{\_}{Y}} \right)^{2}}},$the regression sum of squares.

${{SS}_{err} = {\sum\limits_{i}\left( {y_{i} - y_{i}^{*}} \right)^{2}}},$the sum of squares residuals

The R² value is calculated as follows:

$R^{2} = {1 - \frac{{SS}_{err}}{{SS}_{tot}}}$

The LM metric (represented by LM-new) is the R2 value calculated asshown above, where 0≦LM≦1. The closer the value of LM to 1, the morelinear the access pattern is. This computed LM (represented by LM-new)is passed to an adjustment module 210 (tuning algorithm)).

Once the linearity metrics 216 are computed the adjustment module 210tunes one or more tunable parameters 218. Tuning adjustment may includeother methods to adjust tunable parameters of an SSD using the usagehistory. Illustrative embodiments may include making a decision foradjustment by studying the trends in metric vectors, computing theamount of adjustment of the tunable parameters based on the metricvectors, etc. In one embodiment, a method for tuning a tunable parameterincludes tuning a number of log blocks in a hybrid FTL algorithm. Anexample of this method is as follows.

Pseudocode for Tuning Adjustment:

   Input: Linearity Metric (LM) for a past time interval (computed asshown above) = LM-new    System Constants: Total No of Blocks = B   Tunable System Parameter: No. of Log Blocks = B_(L) [Note: Number ofData Blocks = B_(D) will implicitly become: (B − B_(L))]    Parameters:Number of time intervals for which history is maintained = N    DeltaThreshold = Δ    Standard Deviation Threshold = Std_Δ    Adjustment =B_(A)    Minimum Log Blocks = B_(MIN)    Maximum Log Blocks = B_(MAX)   Algorithm State: Let LM-prev represent the linearity metric computedin the last iteration. Let D[1],D[2],.., D[N] represent the differencebetween the successive linearity metrics computed in the past. Thealgorithm stores these values { LM-prev, D[1].. D[N] } values as itsstate.    Algorithm: (Input = LM-new)    Step 1: Compute the latestdifference in linearity metric; Add the latest difference to the historyof differences by erasing the oldest   difference (D[1]). Remember thelatest linearity metric for the next iteration.   D[1] = D[2] //overwriting the oldest difference D[1] with D[2]   D[2] = D[3]   :   .   D[N−1] = D[N]    D[N] = LM-new − LM-prev // computing the latestdifference and storing it in D[N] LM-prev = LM-new  // storing thecurrent linearity metric for next invocation of the algorithm.    Step2: Determine if adjusting the tunable parameter is desired by looking atthe trend in the differences: One way to study the trend is to simplyadd up the differences and note the trend. Other ways may includecounting how many positive differences and how many negative differencesare present. Decisions can be made based on these differences.   Avg =Average Differences = (D[1] + D[2] + ... + D[N]) / N   Std = StandardDeviation of all differences   If ((Avg > Δ) OR (Avg < − Δ)) AND Std <Std_Δ      Adjust = true;   Else      Adjust = false;      If (Adjust =false) Quit;    Step 3: Adjust the tunable parameters:   If (Sum > Δ) //increase the log blocks      B_(L) = Min( B_(L) + B_(A) , B_(MAX)) //but the log blocks cannot exceed B_(MAX)   else   if (Sum < −Δ) //decrease the log blocks      B_(L) = Max( B_(L) − B_(A) , B_(MIN)) //but log blocks cannot go below B_(MIN.)

By making the adjustments to the tunable parameters 218, the memory usedin the flash memory 100 may be controlled to enhance useful lifetime ofthe memory. Internal SSD parameters are dynamically tuned to increase toincrease application performance and lifetime.

In addition to changing the number of data blocks versus log blocks,other internal SSD parameters may be adjusted as well. Some exampleparameters that can be tuned or adjusted in accordance with the presentprinciples may include an adjustment to a number of available logblocks, an adjustment to a number of pages to prefetch, an adjustment toswitch modes between, e.g., block-based and page-based FTLs (in SSDdevices that can support multiple FTL schemes), an adjustment to agranularity of the page size, etc. For example, in adjusting granularityin FTLs that support both 2 k page size and 4 k page size, the linearitymetric can give hints as to when to use smaller pages sizes and when touse larger page size.

In another implementation, the linearity metric can also guide hybridFTL schemes. One example may include making a decision to put workloadswith random accesses in a single level cell (SLC) region and sequentialaccesses in a multiple level cell (MLC) region, since random accessestend to wear out the device more than sequential accesses. Note SLCmemory stores one bit in each cell, leading to faster transfer speeds,lower power consumption and higher cell endurance. MLC memory stores twobits in each cell. By storing more bits per cell, an MLC memory willachieve slower transfer speeds, higher power consumption and lower cellendurance than the SLC memory. This method may be employed with othermemory types as well, e.g., triple memory cells (TLC), etc.

The adjustments called for by the adjustment module 210 may be performedduring downtime or may be performed online (e.g., slowly in anincremental way) without interrupting applications.

It should be understood that reference to a “block” followed by a findnumeral in the flow/block diagrams of FIGS. 4 and 5 does not refer to ablock-sized memory unit. Instead, the blocks as referred to in FIGS. 4and 5 are steps, modules, circuits, etc. as defined above.

Referring to FIG. 4, a block/flow diagram shows a system/method foradjusting SSD parameters in accordance with illustrative embodiments. Inblock 402, a logical to physical (L2P) translation table or otherstorage structure is provided in the FTL of an SSD controller. In block404, a linearity metric vector is computed to determine the linearity ofthe L2P map. The linearity metric may be computed using historical dataover a first period of time as compared to a second period of time. Aregression analysis may be performed to determine the linearity. Othermethods are also contemplated.

In block 406, a computed metric vector is added to a history table. Inblock 408, the history table is employed to determine if any FTL tunableparameter(s) need to be adjusted. Criteria may be provided to indicatethat a significant change or a threshold change has occurred in workloador the like. In block 410, a decision is made as to whether tunableparameters need to be adjusted. If adjustment is needed, block 412computes new FTL tunable parameter values. Historic data or changes indata may be correlated to desired settings for SSD parameters. This maybe provided using a look up table or by computing an algorithm todetermine new values for tunable parameters. In block 414, the FTLtunable parameters are adjusted by the determined amount.

If in block 410, a determination is made that no adjustments are neededor adjustments have be made in block 414, the method sleeps for aninterval. After an interval has elapsed, the method continues with block404.

Referring to FIG. 5, another method for tuning a solid state disk memoryis illustratively depicted. In block 502, a metric representing a usagetrend of a solid state disk memory is computed. The metric may include alinearity metric computed by comparing usage pattern data over at leasttwo time intervals. The metric may be computed using a regressiontechnique or other data analysis technique to compare usage pattern dataover time. A logical to physical translation table or other datastructure (e.g., hash table, tree structure, etc.) may be employed toobtain usage pattern data.

In block 504, a determination is made to as whether a parameter, type ofparameter, combinations of parameters, etc. need to be adjusted or tunedto provide a change in performance. In block 506, metrics or historicchanges in metrics are compared to determine an adjustment type, e.g.,using a lookup table, inputting the metrics or the historic changes intoa formula, etc. In this way a correlation between workload patterns canbe interpreted to determine which adjustment parameters or combinationsof parameters should be altered or tuned.

In block 508, the parameter is adjusted in accordance with the metric(or metric history) to change the performance. The amount of theadjustment may be determined in block 504 and 506, but may be determinedseparately, in block 510, by comparing metrics or historic changes inmetrics to another lookup table to find an adjustment amount or bycomputing an adjustment amount by inputting metrics or historic changesin metrics into another formula. Adjusting the parameter may includeadjusting the parameter of one or more of: a log-like write mechanism, agarbage collector and/or wear-leveling mechanism. The parameter mayinclude of one or more of: a number of data blocks versus log blocks, anumber of pages to prefetch, a block-based or page-based mode, agranularity of memory size, and/or a type of memory access.

In block 512, the parameter adjustment may be dynamically performedduring usage of the solid state disk. This may include performing tasksslowly over time; using low activity intervals to update configure thememory, etc.

In block 514, some or all of blocks 502-512 may be repeated after anelapsed time interval to recheck and determine whether adjustments areneeded after the elapsed time interval. Adjustments are accordinglycarried out as described above.

Having described preferred embodiments for dynamic tuning of internalparameters for solid-state disk based on workload access patterns (whichare intended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope of the invention as outlined by the appended claims.Having thus described aspects of the invention, with the details andparticularity required by the patent laws, what is claimed and desiredprotected by Letters Patent is set forth in the appended claims.

What is claimed is:
 1. A method for tuning a solid state disk memory,comprising: computing a metric representing a usage trend of a solidstate disk memory; determining whether one or more parameters need to beadjusted to provide a change in performance; adjusting the one or moreparameters in accordance with the metric to change the performance; andrepeating the steps of computing, determining and adjusting after anelapsed time interval, wherein computing a metric includes computing alinearity metric by comparing usage pattern data over at least two timeintervals.
 2. The method as recited in claim 1, wherein computing ametric includes employing a regression technique to compare usagepattern data over time.
 3. The method as recited in claim 1, whereincomputing a metric includes employing a logical to physical translationtable to obtain usage pattern data.
 4. The method as recited in claim 1,wherein determining whether one or more parameters need to be adjustedincludes comparing metrics or historic changes in metrics to a lookuptable to determine an adjustment type.
 5. The method as recited in claim1, wherein determining whether one or more parameters need to beadjusted includes computing an adjustment type by inputting metrics orhistoric changes in metrics into a formula.
 6. The method as recited inclaim 1, wherein adjusting the one or more parameters includes comparingmetrics or historic changes in metrics to a lookup table to anadjustment amount.
 7. The method as recited in claim 1, whereinadjusting the one or more parameters includes computing an adjustmentamount by inputting metrics or historic changes in metrics into aformula.
 8. The method as recited in claim 1, wherein adjusting the oneor more parameters includes adjusting the one or more parametersdynamically during usage of the solid state disk.
 9. The method asrecited in claim 1, wherein adjusting the one or more parametersincludes adjusting one or more of: a log block write mechanism, agarbage collector and/or wear-leveling mechanism.
 10. The method asrecited in claim 1, wherein adjusting the one or more parametersincludes adjusting one or more of: a number of data blocks versus logblocks, a number of pages to prefetch, a block-based or page-based mode,a granularity of memory size, and/or a type of flash memory access. 11.A method for tuning a solid state disk memory, comprising: computing alinearity metric by employing a logical to physical translation table toobtain usage pattern data representing a usage trend of a solid statedisk memory over two or more time intervals and comparing the usagepattern data over the two or more time intervals; determining whether aparameter needs to be adjusted to provide a change in performance byconsulting a lookup table or formula; and adjusting the parameter inaccordance with the metric to change the performance.
 12. The method asrecited in claim 11, wherein computing a linearity metric includesemploying a regression technique to compare usage pattern data overtime.
 13. The method as recited in claim 11, wherein determining whethera parameter needs to be adjusted includes comparing metrics or historicchanges in metrics to the lookup table to determine an adjustment type.14. The method as recited in claim 11, wherein determining whether aparameter needs to be adjusted includes computing an adjustment type byinputting metrics or historic changes in metrics into the formula. 15.The method as recited in claim 11, wherein adjusting the parameterincludes determining an adjustment amount by comparing the linearitymetrics in a lookup table of tuning parameters.
 16. The method asrecited in claim 11, wherein adjusting the parameter includesdetermining an adjustment amount by inputting linearity metrics orhistoric changes in metrics into a tuning formula.
 17. The method asrecited in claim 11, wherein adjusting the parameter includes adjustingthe parameter dynamically during usage of the solid state disk.
 18. Themethod as recited in claim 11, wherein adjusting the parameter includesadjusting the parameter of one or more of: a log block write mechanism,a garbage collector and/or wear-leveling mechanism.
 19. The method asrecited in claim 11, wherein adjusting the parameter includes adjustingthe parameter of one or more of: a number of data blocks versus logblocks, a number of pages to prefetch, a block-based or page-based mode,a granularity of memory size and/or a type of flash memory access. 20.The method as recited in claim 11, wherein determining whether aparameter needs to be adjusted includes evaluating a trend indifferences in the linearity metric by counting a number of positivedifferences and a number of negative differences.
 21. A method fortuning a solid state disk memory, comprising: receiving access requestinformation in a solid state disk controller; storing the access requestinformation in a translation table; computing a linearity metric, usinga regression technique, from the access request information in thetranslation table to obtain usage pattern data representing a usagetrend of a solid state disk memory over two or more time intervals andby comparing the usage pattern data over the two or more time intervals;determining whether a parameter needs to be tuned to provide increasedmemory lifetime by consulting a lookup table or formula; adjusting theparameter in accordance with the metric to increase an overall lifetimeof the solid state disk memory; and rechecking whether adjustments areneeded after an elapsed time interval.
 22. The method as recited inclaim 21, wherein adjusting the parameter includes adjusting theparameter dynamically during usage of the solid state disk.
 23. Themethod as recited in claim 21, wherein adjusting the parameter includesadjusting the parameter of one or more of: a log block write mechanism,a garbage collector and/or wear-leveling mechanism.
 24. The method asrecited in claim 21, wherein adjusting the parameter includes adjustingthe parameter of one or more of: a number of data blocks versus logblocks, a number of pages to prefetch, a block-based or page-based mode,a granularity of memory size, and/or a type of memory access.